I am very glad that you think well of the Echinoderm work. Several other experiments have occurred to me to try, and I hope to be able to do so next autumn, as also the interesting experiment suggested by Frank of rotating by clockwork (as you did the plants) an Echinus inverted upon its aboral pole, to see whether it would right itself when the influence of gravity is removed. No doubt I must in my second book deal with instincts of all kinds, complex or otherwise. Your 'speculations' on the sand-wasp seem to me very pithy--excuse the pun suggested by the analogy of the cattle--and I think there can be little doubt that such is the direction in which the explanation is to be sought. I also think that the difficulty is mitigated by the consideration that both the ganglion of the spider and the sting of the wasp are organs situated on the median line of their respective possessors, and therefore that the origin of the instinct may have been determined or assisted by the mere anatomical form of the animals--the wasp not stinging till securely mounted on the spider's back, and when so mounted the sting might naturally strike the ganglion. But I have not yet read Fabre's own account, so this view may not hold. Anyhow, and whatever determining conditions as to origin may have been, it seems to me there can be little doubt that natural selection would have developed it in the way you suggest. I have now grown a number of seeds exposed to the flashing light, but am not yet quite sure as to the result. About one seedling out of ten bends towards the flashing source very decidedly, while all the rest, although exposed to just the same conditions, grow perfectly straight. But I shall, no doubt, find out the reason of this by further trials. It is strange that the same thing happens when I expose other seedlings to constant light of exceedingly dim intensity. It looks as if some individuals were more sensitive to light than others. I do not know whether you found any evidence of this. I have just found that this year again I have been too late in asking them to send me cuttings of the vine for grafting. I did not know that the sap in vines began to run so early. I remain ever yours, very sincerely and most respectfully, GEO. J. ROMANES. _From C. Darwin, Esq., to G. J. Romanes._ Down: April 18, 1881. I am extremely glad of your success with the flashing light. If plants are acted on by light, like some of the lower animals, there is an additional point of interest, as it seems to me, in your results. Most botanists believe that light causes a plant to bend to it in as direct a manner as light affects nitrate of silver.